1. Field of the Invention
The present invention relates to an electromechanical filter having a plurality of mechanically coupled mechanical resonators disposed in parallel with one another, in particular resonators of the flexural vibration type, wherein the first and the last resonators in the direction of transmission are each provided with an electrostrictive transducer element which has a feeder constituted by an insulating bushing mounted in a metallic base plate, and is connected to an electrical input circuit or terminal circuit, respectively, constructed as an LC resonant circuit, the capacitor of the input circuit and of the terminal circuit being disposed within a trough-shaped recess in the base plate beneath the filter.
2. Description of the Prior Art
Electromechanical filters have assumed great practical importance in resolving many problems which arise in filter technology among other things insofar as such filters are known to be superior in some respects to filters constructed from concentrated circuit elements, both with respect to the space required and with respect to their electrical properties, above all the quality of their resonance elements. Electromechanical filters, in particular those having flexural resonators as resonance elements and coupling elements describing longitudinal vibrations, such as are known for example from the German Pat. No. 1,922,550, have proved highly suitable for use in miniaturized circuits in which the filters also must be as small as possible in volume.
With such mechanical filters, the input and output circuits are constructed as electrical, i.e. LC resonant circuits. Here, the resonant circuit coils, for example on the long sides of the filter cover, and the resonant circuit capacitors are housed most favorably in a trough-shaped recess in the base plate beneath the filter, in particular by virtue of the compact and small filter configuration. This configuration has proved valuable in itself. However, for this configuration, the connecting wires at both capacitors must be manually formed, cut and soldered to a groove in the base plate and to the bushing of the transducer elements.
Because of the cramped conditions, this assembling of the capacitors proves to be relatively difficult and poses problems for automation, particularly when the tolerances for the external dimensions of the capacitors employed are large or when differing capacitors are employed.